Pipette tips are used together with pipetting devices for metering liquids. Pipette tips have an elongate, tubular body which has a pipetting aperture at the lower end and a placement aperture at the upper end for placement on a receiving shank of the pipetting device. The receiving shank is typically of conical shape. However cylindrical receiving shanks or a mixture of forms are also known. Furthermore there are conical or cylindrical receiving shanks which have circumferential bulges or the like to intensify the sealing or clamping action. The pipetting device comprises a gas displacement device, which typically is designed as a piston-and-cylinder unit. The gas displacement device is connected to a through-aperture of the receiving shank. The pipette tip is fixed by forcing the receiving shank of the pipetting device into the placement aperture of the pipette tip on the pipetting device.
By means of the gas displacement device a gas column is displaced to draw liquid into the pipette tip placed on the receiving shank or to expel it from the tip. The gas column is typically an air column. When the gas column is displaced away from the pipette tip, a certain volume of liquid is drawn into the tubular body through the pipetting aperture. By displacing the gas column toward the pipette tip a volume of liquid is dispensed from the tubular body through the pipetting aperture.
There are pipetting devices in which the pipette tip is lifted off manually from the receiving shank. Typical pipetting devices have a throw-off device which acts on the upper edge of the pipette tip to force it off from the receiving shank.
The pipetting device can be a hand-operated pipette or a metering station, the gas displacement device able to be actuated by hand or driven by a motor. The placement and throw-off of the pipette tip can also be manual or driven by a motor.
To avoid faulty pipetting the pipette tip has to be sealingly fixed to the receiving shank. Moreover the forces for placement of the pipette tip on the receiving shank and throwing it off therefrom should not be too large. The contact region between the pipette tip and the receiving shank is of annular form. In the annular contact region the pipette tip is relatively rigid. As a result, the forces for placement and throwing off are already much too large. When thrown off the contact region overall passes simultaneously from cohesive friction to sliding friction. As a result much greater forces have to be applied for throwing off.
Starting therefrom the object of the invention is to produce a pipette tip in which the throw-off forces to release it from a receiving shank are reduced and which has an increased flexibility in the head region.
The object is achieved by a pipette tip with the features of claim 1. Advantageous embodiments of the pipette tip are indicated in the sub claims.